Wireless communication, since its birth 100 years ago, has been serving human beings and has brought convenience to all of us. From early Marconi radio to today's cell phones and TV broadcasting, wireless communication is the symbol of modern life style.
In the past 10 years, wireless technology has been booming in an enormous way. There are many wireless standards associated with variety of wireless products that are making peoples' life easier and convenient. Those standards include cellular standards such as GSM (Global System for Mobile), IS-95 (Interim Standard 95)/CDMA2000 (Code Division Multiple Access 2000), 3GPP/UMTS/LTE, WiMax/IEEE 802.16e and local area networks standards such as WiFi/IEEE 802.11, BlueTooth, Zigbee, and UWB/IEEE 802.15 etc.
Typically, a wireless communication system has four major subsystems, i.e. antenna system, radio system, baseband system and MAC processor. Antenna is responsible to pick a signal or to radiate a signal; radio system will select and regulate the interested signal coming down from an antenna or regulate the signal from baseband subsystem before it goes to the air; baseband is the place where the messages get processed such as encoding/decoding, modulation/demodulation, encryption/decryption, filtering etc.; MAC (media access control) will re-format the messages properly either suitable for transmission or suitable for reception.
Radio system is critical in all wireless communications. Radio design and development rely on almost all the sciences from mathematics, physics to materials and industry manufacturing art. In the past 30 years, radio design and implementation have been in remarkable progress and formed a big portion of wireless industry. However, radio design philosophy has no much fundamental progress. We are still following the traditional steps. In transmission side, baseband subsystem formulates the lower frequency signals. Radio subsystem will up-convert the lower frequency signal to a designated higher frequency signal and then amplify it and radiate it from an antenna. The up-conversion usually is realized in multiple stages a.k.a intermediate frequencies (IF). In the receiver side, it is just reverse the procedures of transmitter, i.e. it will down convert the received signal frequency until baseband subsystem can handle it.
According to wave propagation theory, with the same power, lower frequency can propagate longer distance than higher frequency.
In order to transmit longer distance in high frequencies, directional antenna and power amplifier (PA) have to be equipped. On the other hand, using low frequencies need larger dimensional antenna to achieve the optimal transmission and reception. Therefore there is a dilemma for cellular industry. One side people prefer smaller cell phones for portability reasons. On the other side, people like a longer reach so that less base stations needed to build a cellular network. There is an industry trend that broadband cellular systems should move to lower frequency band, i.e. the spectrum below 1 GHz. This kind of frequency re-farming makes the cell phone design a big challenge. It is very common that a handheld has multiple radios built in already. Future's new frequency release will force cell phone makers to integrate more radios into a handheld. It is not only a big waste in building materials, but also a big challenge both in technology and in economy. It may cause health concerns by pointing multiple radios to the brain when making calls.
It is therefore an object of the invention to provide a system and apparatus to make the handheld design less dependent on frequencies changes or independent on frequencies changes.
The foregoing embodiments and advantages of the invention are illustrative that can be implemented by the various exemplary embodiments and are not intended to be exhaustive. Thus, these and other embodiments and advantages of the various exemplary embodiments will be apparent from the illustrations and examples herein or can be learned from the various exemplary embodiments, both as embodied herein or as modified in terms of any variation that are apparent to those persons skilled in the art.